A wireless power system employs a pair of inductive coils forming a loosely-coupled transformer to transfer power wirelessly. The pair of inductive coils includes a transmit coil formed, for example, as a portion of a charging pad, and a receive coil integrated with an electronic device such as a mobile phone, smartphone, or other computing device. Power transferred to the receive coil may be used by the electronic device to, for example, charge a battery of the electronic device.
FIG. 1 illustrates a wireless power system that includes a wireless power transmitter 2 and a wireless power receiver 3. The wireless power transmitter 2 receives a fixed voltage from a DC adapter. The fixed adapter voltage is scaled by a DC/DC converter 4 and applied to an inverter 6. The inverter, in conjunction with transmitter matching network 8, generates an AC current in transmit coil 10. The AC current in the transmit coil 10 generates an oscillating magnetic field in accordance with Ampere's law. The oscillating magnetic field induces an AC voltage into the tuned receive coil 12 of wireless power receiver 3 in accordance with Faraday's law. The AC voltage induced in the receive coil 12 is applied to a rectifier 16 that generates an unregulated DC voltage. The unregulated DC voltage is regulated using a DC/DC converter 18, which is filtered and provided to a load, such as a battery charger of an electronic device.